Waste disposal

ABSTRACT

Burning a waste fuel blend at very high temperatures (typically greater than 4000 deg. F.) for a very short period of time (typically a matter of milliseconds) in a primary combustion zone to break the complex hazardous/toxic hydrocarbons into less complex chemicals (such as CO, CO 2 , H 2 , OH, HCl, and Cl 2 ), passing the products of the primary zone into a secondary zone in which the products are maintained for a longer time (typically about 2 secs.) in turbulent conditions with excess air at lower combustion temperatures (typically 2000 to 2600 deg. F.) to reduce the primary zone products to a mixture of H 2  O, CO 2  and acids such as HCl, and quenching the products of the secondary zone.

This application is a division of application Ser. No. 336,251, filedDec. 31, 1981, now U.S. Pat. No. 4,462,318.

This invention relates to waste and, more particularly, to a hightemperature system for processing RCRA wastes.

A primary object of the present invention is to provide a system forreducing liquid and slurry hazardous or toxic hydrocarbon wastes, suchas PCB's, to non-hazardous by-products, such as water and simple acids.Other objects include providing such systems which will meetenvironmental requirements, are portable, and will handle a variety ofhazardous and toxic materials.

The invention features burning a waste fuel blend at very hightemperatures (typically greater than 4000 deg. F.) for a very shortperiod of time (typically a matter of milliseconds) in a primarycombustion zone to break the complex hazardous/toxic hydrocarbons intoless complex chemicals (such as CO, CO₂, H₂, OH, HCl, and Cl₂), passingthe products of the primary zone into a secondary zone in which theproduct is maintained for a longer time (typically about 2 secs.) inturbulent conditions with excess air at lower combustion temperatures(typically 2000 to 2600 deg. F.) to reduce the primary zone products toa mixture of H₂ O, CO₂ and acids such as HCl, and quenching the productsof the secondary zone. Preferred embodiments feature fuel-richcombustion in the primary zone to reduce the production of oxides ofnitrogen, scrubbing the secondary zone output after quench to neutralizeacids, and a water spray into the outlet from the secondary zone both toreduce temperature and to insure that any free Cl₂ is changed to HCl. Insuch preferred embodiments, the peripheral wall of the secondary zone isheld above the dew point of HCl (about 500° F.), a negative pressure ismaintained in both the primary and secondary combustion zones, and thediameter of the secondary zone is at least twice that of the primaryzone to insure turbulent expansion into the former.

Other objects, features and advantages will appear from the followingdetailed description of a preferred embodiment of the invention, takentogether with the attached drawings in which:

FIG. 1 is a plan schematic of a mobil waste treatment system embodyingthe invention;

FIG. 2 is a side elevation of a portion of the system of FIG. 1;

FIGS. 3-5 are sectional views of portions of the system of FIG. 1;

FIG. 6 is a broken view, partially in section, of a portion of thesystem of FIG. 1; and,

FIGS. 7-9 are schematics of portions of the system of FIG. 1.

STRUCTURE

Referring now to the drawings, and particularly to FIGS. 1 and 2, thereis shown a mobile liquid incineration system mounted on threeinterconnected trailers. Combustion trailer 10 mounts the primarycombustor 12 and secondary combustor 14, the quench system 16, a masstransfer scrubber 18 (Ceilcote Co.), a discharge fan 17, and a stack 19(Ceilcote Co.). Ancillary trailer 20 mounts a pair of 2000 gallonwaste/blend feed tanks 22, a 2000 gallon kerosene fuel tank 24, and apair of cooling towers 26 (Baltimore Aircoil Co. Model No. VXT-75). Thethree tanks 22, 24 are mounted in a spill containment pan 28 having atotal capacity of about 2500 gallons. The system control room 32, a 2000gallon caustic feed tank 34, and a 4000 gallon waste caustic tank 36 aremounted on laboratory trailer 30. Each trailer is a Great Dane, ModelNo. GP-45, 45 feet long and 8 feet wide. The system includes also an11,000 gallon liquid oxygen tank 40 which, for safety, is mounted at adistance from trailers 10, 20 and 30.

Primary combustor 12 includes a burner plate assembly 112 at its inletend, a central combustion section 114, and at its outlet end a primaryoutlet/secondary inlet assembly 116. The burner plate assembly 112,central section 114 and outlet/inlet assembly are bolted together inaxial alignment with each other and with secondary combustor 14.

Burner plate assembly 112 is shown most clearly in FIGS. 3 and 4. Asthere shown, it includes a burner plate 118 mounted on the end ofcentral section 114 and having an axial fuel/waste inlet nozzle 120directed into the central section and connected through a drilled roundbar 122 to a tapped inlet 124. A coaxial air/oxygen pipe 126 surroundsbar 122 and is connected, through elbow section 128, to a flanged inlet130. Nine triangular ports 132, arranged in a circle around nozzle 120,provide for air/oxygen flow from pipe 126 into central section 114, andinclined vanes 134 are attached to the rear of plate 118 at theradially-extending sides of ports 132 to impart a swirl to theair/oxygen flow.

Burner plate assembly 112 includes also a cooling water jacket 136 forcooling the portion of plate 118 between ports 132 and the cylindricalwall of central section 114, an inlet 138 into the water jacket, and anoutlet 140 surrounding an inclined viewing port 142 for a flame detector143 (see FIG. 8). An inclined ignitor port 144, circumferentially spacedabout 60 degrees from viewing port 142, permits a propane ignitor to beinserted into central section 114.

Central section 114 includes an inner cylinder 152 of Inconel 625 steelsurrounded by a carbon steel water jacket 154. There is a water gap 156of about 1/8 in. between cylinder 152 and water jacket 154. Flanges 158,158a each defining twelve radially extending conduits defining,respectively, water outlets 159 and water inlets 160 are mounted atopposite ends of the combustor.

Outlet/inlet section 116 similarly includes an inner cylindrical shell162 of Inconel 625 (11 5/8" diameter) steel surrounded by a water jacket164 to provide an intermediate water gap 166. A flange 168,substantially identical to flanges 158, 158A of central section 114, isprovided at the end of outlet/inlet section nearest central section 114.Intermediate the length of outlet/inlet section 116 is a second flange169, of greater diameter than flange 168. Flange 169 is bolted to theend of secondary combustor 14, and the portion of inlet/outlet section116 on the side of flange 169 opposite flange 168 thus is withinsecondary combustor 14. A larger diameter water jacket 172, the exteriorof which is defined by Inconel 625 steel, surrounds the portion ofoutlet/inlet section within secondary combustor 14. Cooling water entersthrough twelve conduits defining inlets 170 in the flange 168 and flowsthrough water gap 166 to the end of outlet/inlet section 116 withinsecondary combustor. The water then flows radially into the largerdiameter water jacket 172, and then in the other direction back toflange 169 where it exits through four spaced outlet pipes 174.

Referring now to FIG. 2, secondary combustor 14 comprises a steel tube176, about 54 in. in diameter and 241/2 feet long, supported by a pairof steel rings 178. The interior of tube 176 is lined with refractory180 (A. P. Green Co., Kruzite "D"), the thickness of the refractorylayer typically being about 5 inches, leaving within secondary combustor14 a cylindrical burn zone about 44 in. in diameter. Outlet/inletassembly 116 of primary combustor 12 is attached to a steel end plate184 and a similar end plate 186 is attached to the outlet end of tube176. The inner sides of end plates 184 and 186 are lined withrefractory. A pair of tangential inlets 188, each defined by a 4 in. by6 in. by about 2 ft. long duct of Inconel 625 steel and spaced 180° fromthe other, are provided about 1 foot from the inlet end of combustor 14,with the sides of the inlets nearest end plate 184 aligned with, orspaced but a short distance axially from, the end of outlet/inletassembly 114.

An exit nozzle assembly 190 is mounted on outlet end plate 186, half inand half out of tube 176. As shown most clearly in FIG. 5, exit nozzleassembly 190 includes an outer tube 191 of Inconel 625 steel to which iswelded a flange 192 bolted to end plate 186. The portion of assembly 190within tube 176 includes a converging throat 194 of Inconel 625 steelsurrounded by a cooling water jacket 196. The small diameter end 193 ofthroat 194 is within outer tube 190, a little over two-thirds of the wayfrom the inlet end 198 of tube 190, and mounts six circumferentiallyspaced spray nozzles 200 (1/8 BX-8 Whirljet Nozzle 316). The inlet toeach nozzle 200 communicates with the water gap 204 between water jacket196 and throat 194, and the nozzles are positioned with their sprayoutlets directed axially-along, and at a 15 degree angle towards thecenter of, the exit nozzle assembly. Flow to the water gap 204 andnozzles 200 is provided by a pair of diametrically spaced inlet pipes206. Inlet and outlet pipes 208 provide for water flow to a water gap210 between the portion of outer tube 191 exposed to hot gases (i.e.,downstream of throat end 193) and the outer water jacket 212.

As shown in FIGS. 2 and 8, an air-cooled shroud, comprising a thin steelcylinder 214 about 58 inches in diameter having an air inlet 211 of theend nearest primary combustor 12 and an air outlet 213 at its other end,surrounds tube 176 and its end plates. There is an air flow cap of about2 in. between the inside of cylinder 214 and the exterior of tube 176.

Quench system 16 (see FIGS. 2, 6 and 9) includes a sump 216, about 57in. long, 24 in. wide and 22 in. high, having a top plate 218 definingan inlet 220 and an outlet 222. A 90 degree elbow 224 extends from theoutlet of exit assembly 190 to sump inlet 220. Elbow 224 includes aninner jacket 226 and outer jacket 228 forming a cooling water gaptherebetween and having an outlet 230. Five circumferentially-spaced,radially-inwardly directed nozzles 232, are provided at the inlet end ofelbow 224; five more such nozzles 233 are mounted intermediate thelength of the elbow.

As shown in FIG. 9, a drain 234 and a sump outlet 235, connected to asump pump 236, are provided at the bottom of sump 216. The outlet fromsump 216 is connected, through contact molded tee 238, to mass transferscrubber 18. A safety relief valve 240 is provided at the top of tee238. A recirculation pump 242 is connected between the sump and spraynozzles 244 of transfer scrubber 18. Conduits connect recirculation pump242 also to spent caustic storage tank 36, for discharge of spentcaustic; and a caustic feed and metering pump 250 is provided forintroducing new caustic from tank 34 to spray scrubber 18.

OPERATION

Referring to FIGS. 7 through 9, transfer pump 302 pumps the PCB or otherhazardous/toxic waste to be disposed of from a customer-supplied 55gallon drum 300 through filter 304 to one of tanks 22. The amount offlow is metered by a metering system 306. In tanks 22, the PCB isblended with kerosene from tank 24, so that the blend will have a fuelvalue of at least about 12,000 BTU/lb.; and the blend is pumped throughpump heater 314 and duplex pump/filter 316, through nozzle inlet 124into primary combustor 12. The rate of flow is controlled by flowcontrol 317.

Typically, a prepared waste/kerosene blend is withdrawn from one oftanks 22 while the blend is being prepared, i.e., the waste and fuel aremixed in the proper predetermined proportions, in the other tank 22.During blending, kerosene from fuel tank 24 is pumped by pump 310through filter 312, and waste from tank 300 is pumped by pump 302through filter 304, into the blend tank 22. The flow of kerosene andwaste is precisely controlled by metering systems 308, 306.

An oxygen/ambient air mixture is pumped into primary combustor 12through inlet 130. The oxygen flow from tank 40 is controlled by valve41, the ambient air is provided by a primary air blower 324, the flowfrom which is controlled by damper 336. A secondary air blower 328, theflow from which is controlled by damper 330 provides the air intosecondary combustor 14. Backflow into the secondary air system isprevented by flame arrester 332.

For initially igniting the PCB/kerosene mixture, a propane torch ignitor322, connected to regulated propane 318 and air supplies 320, isinserted into primary combustor 14 through ignitor port 144.

Cooling water to the primary combustor is provided by a cold watersupply pump 340. As illustrated in FIG. 8 the water enters the inlets138, 160 and 170 to cool the primary combustor and exits through theoutlets 140, 159, and 170 through respective valves 342, 344, 346 whichcontrol the respective flows of water and thus the temperature withinthe cooling jackets 136, 154 and 172 respectively. Cooling air to thesecondary combustion chamber is pumped into the inlet 211 from acompressor 348 which receives ambient air through a valve 350, the valve350 controlling the amount of air supplied and thus the temperaturewithin the air gap between the tube 176 and the cylinder 214.

In typical operation, the PCB/kerosene mixture sprayed into primarycombustor 12 is a 50:50 mixture, and is supplied at a rate of about408.73 pounds of each per hour. Oxygen from tank 40 and ambient air aresupplied at rates, respectively, of 1054 and 1951.70 pounds per hour.About 170,056 lbs of cooling water are pumped through the primarycombustor's water jackets each hour; the cooling air flow through theair jacket surrounding tank 176 of secondary combustor 14 is about33,493 lbs/hr; and air is injected tangentially into secondary combustor14 through ports 188 at a flow rate of about 2033 lbs/hr.

In primary combustor 12, the PCB/kerosene burns, in an oxygen-enrichedair atmosphere at sub-stoichometric conditions (e.g. 0.8 stoichometric;a fuel-rich atmosphere), at a temperature ranging from about 4500 deg.F. at the combustor inlet to about 2600 deg. F. at the outlet. Thetemperature drop is controlled by the cooling water flow. The burningmixture is maintained in the primary combustor for a very short time,e.g., for a matter of milliseconds; but this short time-high temperaturecombustion has, unexpectedly, been found to accomplish substantiallycomplete destruction of the PCB's, converting them into a mixture of OH,CO, CO₂, H₂, H₂ O, Cl₂ and HCl.

A typical output of the primary combustor, into the secondary combustoris:

a. OH: 50.08 lbs/hr

b. CO: 708.43 lbs/hr

c. CO₂ : 831.15 lbs/hr

d. H₂ : 11.09 lbs/hr

e. H₂ O: 412.14 lbs/hr

f. NO: 27.14 lbs/hr

g. Cl₂ : 53.14 lbs/hr

h. HCl: 173.57 lbs/hr

i. O₂ : 69.20 lbs/hr

j. N₂ : 1487.20 lbs/hr.

As can be seen, one significant advantage of the high-temperature/shorttime/sub-stoichometric combustion in primary combustor 12 is a very lowlevel of nitric oxide (NO). The less than stoichometric conditions(e.g., about 0.80 stoichometric) results also in a higher burningtemperature. The temperature of the inner wall of primary combustor 12is maintained well above the dew point (about 500 deg. F.) of HCl tominimize corrosion.

The diameter of secondary combustor 14 is much greater than that ofprimary combustor 12 (in the illustrated embodiment the inner diameterof primary combustor is 115/8 in. and that of secondary combustor isabout 44 inches; the preferred ratio being, thus being about 4:1 and theratio always being greater than about 2.5:1); and the high temperaturegasses thus undergo turbulent expansion as they are discharged into thesecondary combustor. The desired turbulence is obtained by the fact thatvanes 134 impart a right-hand swirl to the air/oxygen mixture injectedinto primary combustor 12, while secondary combustor tangential inlets188 impart a reverse swirl to the air injected through them into thesecondary combustor 14.

In secondary combustor 14, the mixture of gases from primary combustor12 burns at in an excess air atmosphere (e.g., 1.05 stoichometric) for amuch longer period (typically the dwell time in the secondary combustoris about 2 seconds) at lower temperatures, typically in the range of2000° to 2600° F. near the inlet and about 2200° to 2300° F. at theoutlet. The amount of air injected into secondary combustor throughtangential inlets 188 is, typically, 2033 lbs/hr at a velocity of about200 feet per second. As in primary combustor 14, the inner refractorywall of combustor 14 is maintained above the dew point of HCl.Typically, the outlet product from secondary combustor 14 is:

a. CO₂ : 1944.36 lbs/hr

b. H₂ O: 525.00 lbs/hr

c. NO: 5.09 lbs/hr

d. HCl: 228.20 lbs/hr

e. O₂ : 93.73 lbs/hr

f. N₂ : 3059.78 lbs/hr.

As can thus be seen, the reaction within secondary combustor 14substantially eliminates the OH, CO, H₂ and Cl₂ from the input fromprimary combustor 12, and reduces also the amount of NO.

The product exiting from secondary combustor 14 is quenched with a waterspray (typically 3229.2 lbs/hr) in exit nozzle assembly 190 and inquench elbow 224, dropping the temperature of the product and resultingin adiabatic saturation of the gas at a temperature of about 185° F. Theresulting HCl liquid is scrubbed with NaOH (from caustic tank 34 at arate of about 263 lbs/hr.) in scrubber 18, converting the acid to NaClwhich is purged to tank 36. The remaining product, i.e., a mixture ofCO₂, H₂ O, O₂, N₂ and a small amount of NO, exits the system throughstack 19.

Blower 17 maintains a slightly negative (relative to atmospheric)pressure throughout the system.

The flow of cooling water through the water jacket of primary combustorand of air through the air gap surrounding tube 176 of secondarycombustor 14 are controlled so that (i) the temperatures of thecylindrical inner walls of the two combustors will stay above the dewpoint of HCl and (ii) the temperatures at the outlet of each combustorwill be less, by the desired amount, than that at the inlet.

Numerous alterations of the structure herein disclosed will suggestthemselves to those skilled in the art. However, it is to be understoodthat the present disclosure relates to the preferred embodiments of theinvention which is for purposess of illustration only and not tobeconstrued as a limitation of the invention. All such modificationswhich do not depart from the spirit of the invention are intended to beincluded within the scope of the appended claims.

What is claimed is:
 1. The method for reducing liquid and slurryhazardous waste to non-hazardous by-products, comprising: blending thewaste with a fuel to obtain a blend of liquid fuel and waste having apredetermined minimum fuel value; feeding said blend to a primarycombustor; feeding oxygen-enriched air to said primary combustor in anamount such that a fuel rich-atmosphere is provided in said combustor;imparting a rotational swirl in a first direction to saidoxygen-enriched air; mixing and burning said blend together with saidoxygen-enriched air to obtain a swirling flame in the primary combustorfor a relatively short duration at a high temperature; exhausting theproducts of combustion from said primary combustor to a secondarycombustor; feeding secondary air to said secondary combustor in anamount such that an oxygen-rich atmosphere is provided therein, andimparting rotation to said secondary air when entering said secondarycombustor in a direction opposite to the rotational direction of theproducts of combustion entering the secondary combustor; mixing saidproducts of combustion with said secondary air to reduce the rotationalswirl thereof while burning said products of combustion with saidsecondary air for a substantially long duration at a lower temperaturethan in the primary combustor; controlling the flow rate at which thewaste/fuel blend and the oxygen-enriched air are introduced into theprimary combustor and the rate at which the air is introduced into thesecondary combustor; and quenching the products exiting from thesecondary combustor by spraying water into the products.
 2. The methodas recited in claim 1, wherein said waste is a PCB and the temperaturein said primary combustor is approximately 4000° F. and the temperaturein said secondary combustor is in the range of 2000° F. to 2600° F. 3.In the method as recited in claim 2, wherein said waste/fuel blend has aheat value of not less than about 12,000 BTU per pound.